<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <div>
        <ul>
            <li>111</li>
            <li>222</li>
            <li>333</li>
        </ul>
        <button>删除</button>
    </div>
    <script>
        var ul = document.querySelector('ul');
        var btn  = document.querySelector('button');
        btn.onclick = function(){
            if(ul.children.length == 0){
                this.disabled = true;

            }else
            ul.removeChild(ul.children[0]);
        }
        
    </script>
</body>
</html>